The present invention relates to an optical amplifying glass. Particularly, it relates to an optical amplifying glass capable of amplification in a broad band range for lights with wavelengths of from 1.4 to 1.5 xcexcm.
For the purpose of application to an optical amplifier in an optical communication system, there have been research and development of an optical amplifying glass comprising a core glass and a clad glass and having a rare earth element incorporated to the core glass.
On the other hand, to cope with diversification of communication services expected in future, a wavelength division multiplexing communication system (WDM) has been proposed to increase the transmission capacity. In WDM, the transmission capacity will increase, as the number of wavelength division multiplexing channels increases.
Heretofore, an Er (erbium)-doped optical amplifying glass has been proposed as a glass suitable for optical amplification of C band (wavelength: 1,530 to 1,560 nm) or L band (wavelength: 1,570 to 1,600 nm), and a Tm (thulium)-doped optical amplifying glass has been proposed as a glass suitable for optical amplification of S+ band (wavelength: 1,450 to 1,490 nm) and S band (wavelength: 1,490 to 1,530 nm).
To the Tm-doped optical amplifying glass, an excitation light is introduced together with a light to be amplified i.e. a signal light, and the signal light will be amplified by means of a stimulated emission transition of Tm. The wavelength of the excitation light is typically from 1.0 to 1.6 xcexcm, when excitation is carried out by an upconversion method. Further, the Tm-doped optical amplifying glass is usually used in the form of a fiber.
In the Tm-doped optical amplifying glass, optical amplification of S+band is carried out by means of the stimulated emission transfer between 3H4-3F4. However, below the 3H4 level, there is a near level 3H5 at a distance of about 4,300 cmxe2x88x921. When the phonon energy of the glass containing Tm3+ is large, due to this level 3H5, the multiphonon relaxation in the above-mentioned stimulated emission transfer, increases, and the radiation relaxation decreases, whereby the emission efficiency, accordingly, the optical amplification factor, may decrease.
As a Tm-doped optical amplifying glass, an optical amplifying glass having Tm doped to a fluoride glass (a fluoride type Tm-doped optical amplifying glass) has been proposed. The fluoride glass has a merit such that the multiphonon relaxation is less than an oxide glass. However, the glass transition point Tg of the fluoride type Tm-doped optical amplifying glass is low (typically not higher than 320xc2x0 C.), and it was likely to be thermally damaged, when the intensity of the excitation light was high.
Further, the Vickers hardness Hv of the fluoride type Tm-doped optical amplifying glass is low (typically, 2.4 GPa), whereby it was susceptible to scratching, and when it is made into a fiber, such a scratch is likely to cause breakage.
As an optical amplifying glass having Tm doped to a fluoride glass, a Tm-doped fluoride glass ZBLAN is, for example, known which has 1.19% by mass percentage of Tm doped to a matrix glass of a composition, as represented by mol %, comprising 52.53% of ZrF4, 20.20% of BaF2, 3.03% of LaF3, 4.04% of AlF3 and 20.20% of NaF and which has a Tg of 200xc2x0 C., a peak wavelength of the emission spectrum of 1,452 nm and a half value thereof being 76 nm (Applied Optics, 39(27), 4,979-4,984 (2000)).
Further, as an optical amplifying glass having Tm doped to a tellurite glass, a Tm-doped terlite glass is, for example, known which has 1.23% by mass percentage of Tm doped to a matrix glass with a composition, as represented by mol %, comprising 75% of TeO2, 10% of ZnO and 15% of Na2O and which has a peak wavelength of the emission spectrum of 1,458 nm and a half value width thereof being 114 nm. However, its Tg is as low as 295xc2x0 C. (Applied Optics, 39(27), 4,979-4,984 (2000)).
Further, a glass having 0.01%, 0.05% or 1.5% by outer mass percentage of Tm doped to a matrix glass comprising 56 mol % of PbO, 27 mol % of Bi2O3 and 17 mol % of Ga2O3 (Tm-doped PbOxe2x80x94Bi2O3xe2x80x94Ga2O3 glass) is disclosed (Applied Optics, 34(21), 4,284-4,289 (1995)).
The annealing point and the Knoop hardness of the above matrix glass are 319xc2x0 C. and 2.2 GPa, respectively (Phys. Chem. Glasses, 27, 119-123 (1986)). The annealing, point may be deemed to be equal to Tg, and it is considered that there will be no substantial change in Tg even if Tm is doped up to 1.5%. Namely, Tg of the above Tm-doped PbOxe2x80x94Bi2O3xe2x80x94Ga2O3 glass is also about 320xc2x0 C., whereby the above-mentioned thermal damage is likely to result.
Further, in the case of an optical glass, the Knoop hardness gives a value lower by from 0.4 to 1.3 GPa than Hv (Dictionary of Glass, p. 352, published by Asakura Shoten, 1985). Accordingly, Hv of the above Tm-doped PbOxe2x80x94Bi2O3xe2x80x94Ga2O3 is considered to be within a range of from 2.6 to 3.5 GPa and can not be said to be high.
It is an object of the present invention to provide an optical amplifying glass which has high Tg and Hv and which is capable of amplifying lights in S+ band and S band.
The present invention provides an optical amplifying glass comprising a matrix glass and from 0.001 to 10% by mass percentage of Tm doped to the matrix glass, wherein the matrix glass contains from 15 to 80 mol % of Bi2O3 and further contains at least one component selected from the group consisting of SiO2, B2O3 and GeO2.